Electron transfer in biological systems and the oxidation and reduction of various substrates in living organisms are of fundamental importance to life sustaining processes. Multi- electron transfer processes, although less frequent in nature are of equally great importance. Included among the latter are: The 4e- oxidation of 2H20 to 02 in photosynthesis, the 6e- reductions of N2 to ammonia in nitrogenase, and the 6e- reduction of sulfite to sulfide and of nitrite to ammonia in sulfite and nitrite reductases respectively. Outstanding among the enzymes involved in the oxidation or hydroxylation of substrates is methane monooxygenase, MMO. This enzyme catalyzes the oxidation of methane to methanol at an active site that, unlike cytochrome P- 450, does not utilize an Fe-porphyrin center. This proposal is concerned with the synthesis and study of synthetic analogs for a) metalloenzymes involved in multielectron reduction and b) the non-porhyrin centers active in the oxidation and hydroxylation of organic substrates. Specifically: the synthesis, structures, spectroscopic properties and reactivities of Fe/M/S (M=mo, W, V) and Fe/S clusters are expected to serve as synthetic analogs for the Fe/M/S centers in the nitrogenases and alternate nitrogenases that contain vanadium or iron in place of molybdenum. The new types of Fe/S clusters that will be synthesized are designed as models for the P-clusters of nitrogenase. Supramolecular assemblies with appended Fe/S clusters will be synthesized as possible models for the active sites in sulfite and nitrite reductase. Oligomeric complexes are known, or believed to be, involved in processes such as the oxidation of CH4 to methanol in MMO (M =Fe) and the photosynthetic oxidation of water to 02(M -Mn). Monomeric, mixed-ligand carboxylate complexes also are involved in enzymatic oxidations such as the oxidation of the catechol function to cis muconic acid and the aromatic ring hydroxylation of phenylalanine to tyrosine via reaction with dioxygen, (M =Fe). Carboxylate complexes of first row elements will be studied as structure and reactivity models for the active sites in enzymes that catalyze the oxidation of various substrates.